1. Field of the Invention
The invention relates to a substrate cleaning apparatus and a substrate cleaning method of cleaning a substrate that has one principal surface on which pattern elements are formed and another principal surface to be cleaned. Note that substrates to be cleaned include semiconductor wafers, glass substrates for photo mask, glass substrates for liquid crystal display, glass substrates for plasma display, substrates for FED (Field Emission Display), substrates for optical disc, substrates for magnetic disc, substrates for opto-magnetic disc and various other substrates.
2. Description of the Related Art
A process of manufacturing an electronic component such as a semiconductor device or a liquid crystal display device includes a process of forming fine pattern elements by repeatedly applying processings such as film formation and etching to a top surface of a substrate. Here, if particles are adhering to an under surface of this substrate, they cause defocusing in a photolithography process and it becomes difficult to form desired fine pattern elements. Further, cross-contamination may occur due to a substrate having particles adhering to the under surface.
Further, an under surface of a substrate is often vacuum-sucked during substrate conveyance and particles may adhere to the under surface of the substrate in that process. Thus, numeral technologies for cleaning an under surface of a substrate have been proposed. For example, an apparatus described in JP2010-27816A performs ultrasonic cleaning by supplying an ultrasonic treatment liquid obtained by applying ultrasonic waves to a treatment liquid to an under surface of a substrate. Further, in this apparatus, pattern elements are reinforced by freezing a liquid film formed on a top surface of the substrate in order to prevent the pattern elements formed on the top surface of the substrate from being damaged by ultrasonic waves transmitted to the top surface side of the substrate during ultrasonic cleaning.
The apparatus described in JP2010-27816A is a cleaning apparatus making use of the principle of generating air bubbles (cavitation bubbles) of a micron size in a cleaning liquid by transmitting ultrasonic vibration to the cleaning liquid. A strong liquid flow is generated in the cleaning liquid in conjunction with motions of the cavitation bubbles such as expansion and collapse, whereby particles adhering to a top surface of a substrate are separated from the substrate top surface and washed away together with the cleaning liquid to clean the substrate top surface.
JP2013-84667A discloses a technology for cleaning the entire top surface and under surface of a substrate by accommodating the substrate in an accommodation section and supplying a degassed treatment liquid into the accommodation section to apply ultrasonic vibration to the treatment liquid for the purpose of suppressing the damage of pattern elements formed on the top surface of the substrate similarly to JP2010-27816A. The amount of generated cavitation bubbles is reduced due to a reduction in dissolved gas concentration in the treatment liquid, thereby suppressing damage on the pattern elements of the substrate.
Further, as another substrate cleaning technology using an ultrasonic treatment liquid, JP2004-363453A discloses an apparatus for cleaning a substrate by supplying an ultrasonic treatment liquid applied with ultrasonic waves to a top surface of the substrate from a nozzle while rotating the substrate. This apparatus moves the nozzle in a predetermined direction while maintaining inclination angles, which a top surface of the substrate and a peripheral edge area of the substrate form an axis of the nozzle, constant. This causes ultrasonic cleaning to be performed while the ultrasonic treatment liquid is sprayed not only to the substrate top surface, but also to the substrate peripheral edge area.